The invention relates to a method of manufacturing a color television display tube having a substantially rectangular display window and a funnel part which is substantially rectangular at its wide end. The rectangular end of the funnel part has two mutually perpendicular axes and a supporting surface for the display window. The funnel part is also provided with marks with respect to which the display window is positioned on the supporting surface of the funnel part.
The invention further relates to a device for carrying out this method, as well as to a color television display tube manufactured according to this method.
In manufacturing color television display tubes it is usual to remove color impurities and convergence errors of the tube by means of a number of correction means. These color impurities and convergence errors are a result of inaccurate adjustment of the various components including the display window, the funnel part, the electron gun and the deflection device relative to each other during assembly of the tube. Also, because of limitations in the accuracy with which the components themselves can be manufactured, the same components are not identical to each other.
Several reference systems are known for the adjustment of the various components of the tube. A typical reference system is disclosed in U.S. Pat. No. 3,971,490. In accordance with this patent, reference surfaces are ground on the funnel part of the tube, the axis of the neck of the funnel part being referenced to the ground reference surfaces. The display window at the circumference thereof comprises reference points with respect to which the display screen is provided on the display window. The display window is positioned on the funnel part by use of the reference points of the display screen and the reference surfaces of the funnel part which are referenced to a common reference R. In this manner the display screen is referenced to the axis of the neck of the funnel part. It is assumed that the effective source of the electron beams which are generated by an electron gun to be provided afterwards in the neck, is situated on the axis of the neck so that this effective source is also referenced to the display screen. When using such a reference system, however, it is necessary for the supporting surface of the funnel part destined for the display window to be perpendicular to the axis of the neck. In practice, however, it has been found that it is almost impossible to grind the supporting surface perpendicularly to an axis with the required accuracy. Furthermore, when using said reference system individual positioning of the deflection device is necessary so as to bring the deflection center determined thereby on the axis of the tube neck. The step of adjusting the deflection device of the funnel part is time-consuming and increases production costs. Therefore there exists a need for a system which minimizes the number of operations and adjustments to position a deflection device on the funnel part of a display tube.